000 AXPZ20 KNHC 200948 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 948 UTC Thu Dec 20 2018 Tropical Weather Discussion for the eastern Pacific Ocean from the Equator to 32N, east of 140W. The following information is based on satellite imagery, weather observations, radar, and meteorological analysis. Based on 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: A cold front moving across the Bay of Campeche will continue moving across the Gulf of Mexico through late today. High pressure building behind the front along the Sierra Madre Oriental in the wake of the front will generate a tight pressure gradient over the area and usher in the next gale force gap wind event. Winds will rapidly increase to gale force by late today and to strong gale force by Fri morning. The plume of strong gap winds will reach about 500 nm to the SW of the Gulf of Tehuantepec by late Fri, with seas building as high as 19 ft within the area of strong winds. The gales will persist through Fri night, then diminish on Sat as the high pressure N of the area weakens and shifts east. Fresh to strong gap winds will then persist across the Gulf of Tehuantepec through Sun. Another gale could be on tap for the Gulf of Tehuantepec Sun night. Gulf of Papagayo Gale Warning: The same front will move into the Caribbean. This pattern will support strong gap winds across the Gulf of Papagayo by late Fri, possibly reaching gale force Fri night and Sat, persisting into Sun. Seas may reach 12 ft up to 90 to 120 nm downstream of the Gulf by early Sun. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A surface trough extends from 09N84W to 05N95W to 05N100W. The intertropical convergence zones extends from 05N100W to 08N140W. Scattered moderate convection is ongoing within 120 nm either side of ITCZ west of 135W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see above for more on the impending gale force gap wind event over the Gulf of Tehuantepec. The main issue off Baja California continues to be long period NW swell propagating into the region. Recent altimeter satellite passes indicated 8 to 10 ft seas off Baja California, they also show higher seas farther west, representing a small area of reinforcing swell approaching the area. This will maintain 10 to 12 ft seas mainly off Baja California Norte through today. The swell will subside tonight, leaving mainly 8 to 11 ft swell over the open waters across the region, subsiding further to less than 8 ft through early Sat. The next round of large swell will reach the Baja offshore waters by late Mon. Meanwhile, 1023 mb high pressure centered near 32N122W is maintaining generally light to gentle breezes over offshore waters, and little change is expected through the period. A relatively tight pressure gradient over the Gulf of California related to 1032 mb high pressure well north of the area over the Great Basin is supporting fresh to strong NW winds across mainly the central Gulf of California. These winds will diminish through today as the pressure pattern weakens. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: A cold front will move across the SW Caribbean on Fri morning. Strong N winds behind the front will funnel through the Gulf of Papagayo, increasing to near gale force by late Fri night. This event will peak on Sat as winds reach minimal gale force. A tight pressure gradient between high pres building behind the front and lower pres in the SW Caribbean will support the continuation of the gap wind event through Sun night. Seas are expected to peak near 12 ft on Sat morning. Winds and seas will gradually diminish Sun night through Mon night. Fresh to locally strong N winds are expected over the Gulf of Panama Sat night through early on Mon. Winds could become strong Sat night and Sun as seas peak around 8 ft. Elsewhere, gentle to moderate winds will persist, with seas in the 4 to 7 ft range. REMAINDER OF THE AREA... A cold front passing 140W currently north of 22N will become diffuse as it moves across the waters north of 22N through Fri. High pressure building behind the front will support an area of fresh strong trade winds from 10N to 15N west of 135W tonight. High pressure of 1027 mb is centered north of the area near 34N126W. The pressure gradient between this area of high pressure and lower pressure in the vicinity of the ITCZ will support moderate to fresh trade winds north of the ITCZ to around 20N. A sharp upper-level trough near 155W will eventually cut off near 145w and induce a nearly stationary trough along the ITCZ just west of 140W by Fri afternoon. This will tighten the pressure gradient further in this area. Trade winds will increase from fresh to strong N of the ITCZ to near 15N and west of 135W late Thu through Mon night. NW swell continues to prevail across the discussion area. Seas of 8 ft or greater are noted W of 95W, with a reinforcing set of seas 12 to 14 ft spreading ahead of the cold front. Seas will subside N of 20N and W of 120W tonight through Sat. An area of confused seas will develop by late Sat as a result of lingering NW swell mixing with shorter period swell from Tehuantepec and Papagayo gap events. This will be mainly south of 15N between 100W and 110W. $$ Christensen